In a hybrid electric vehicle comprising an internal combustion engine and an electric motor, an electric vehicle (EV) mode in which only the electric motor is used as motive power and a hybrid electric vehicle (HEV) mode in which both the internal combustion engine and the electric motor are used as motive power are selectively applied.
In order to switch from the EV mode to the HEV mode, cranking of the internal combustion engine is performed using an output torque of the electric motor to start the internal combustion engine. The electric motor and the internal combustion engine are connected via a first frictional engagement element.
JP 2007-126082 A published by Japan Patent Office, proposes a method of starting the internal combustion engine during a vehicle traveling at a low vehicle speed by increasing a rotation speed of the electric motor while a second frictional engagement element interposed between the electric motor and the drive wheel slips. The internal combustion engine and the electric motor are connected to each other via a first frictional engagement element. Herein, each of the frictional engagement elements is constituted by a clutch.